Biology Help: The Immune System - By: johana

In this article Biology Help will be looking at one particular element of the human immune system namely, the innate immune system. The etymology of immunity consists of the Latin word "Immunis" which means ‘exempt’ or ‘freedom’. From a biological perspective, immunity refers to all those mechanisms used by the body to protect itself from threats and/or foreign elements. These include microorganisms or their products, certain food items, chemicals, drugs and pollen, etc.

Immunity in human biology is of two types: Innate and Acquired. Innate immunity refers to the protective mechanisms one is born with and which is always present in the human body. The first line of defence consists of various barriers that block and/or destroy pathogens as they try to enter the body. These barriers are of four types: (a) anatomical, (b) physiological, (c) phagocytic and (d) inflammatory barriers. Anatomical barriers consist of the skin and mucus membranes and act to prevent foreign matter from entering the body. The mucous traps these foreign microorganisms and the cilia (minute hair-like protrusions) propel them out of the body.

Physiological barriers refer to factors such as body temperature, pH and various body secretions, which prevent the growth of many harmful micro-organisms. For example, the acidity of the stomach kills most ingested micro-organisms. As we see in Biology Help, Lysozyme, a protein present in secretions such as tears and saliva acts as an anti-bacterial agent by attacking and digesting bacterial cell walls. Similarly, some of the cells in the body release a type of glycol-proteins called Interferon’s when they’re infected by a virus. Biology Help informs us that the interferon’s act to protect the surrounding non-infected cells by inducing an antiviral state in them and as a result the person exhibits increased resistance to viral infections.

Tissue injury or infection often results in redness and swelling, along with pain and production of heat that may result in fever. Such a manifestation is localised and is known as inflammatory response. The purpose of the inflammatory response is to localize and eliminate the injurious agent and to remove damaged tissue components so that the body can begin to heal. During this process the walls of the blood vessels become more permeable and fluid, proteins and white blood cells migrate to the site of tissue damage. An inflammatory response that lasts only a few days is called acute inflammation, while a response of longer duration is referred to as chronic inflammation.

Phagocytosis is another important mechanism of innate immunity that Biology Help will now examine. Humans contain wandering phagocytes that circulate through the body. These are scavenger cells that destroy foreign material such as microorganisms and debris. Two important phagocytes include the macrophages and the neutrophils. The macrophages are present in many tissues, especially the spleen, the lymph nodes and the liver. As we see in Biology Help, these serve as filters for trapping microbes and other foreign particles that arrive through the blood or the lymph. The neutrophils are stored in the bone marrow and released in response to inflammation or infection. They work by engulfing bacteria and other microorganisms and microscopic particles and digesting them by means of enzymes present in their structure. The aim of this particular article in Biology Help was to give a basic overview of the innate immune system. The system is of course much more complex and will be dealt with in greater detail in other articles in the site.

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